But they do have the same dad.... I'd really like to know how the **** that family came to be.
Were Summer and Dad-man a couple and Yang's mom was a one time threesome participant?
Was Summer a cuck? What the **** happened?!

From what I remember, back in the day, Summer (Rubys mom), Taiyang (Ruby/Yangs dad), Raven (Yangs mom), and Qrow were all part of team STRQ. Since Yang is older it makes more sense that Taiyang was with Raven before Summer, Raven had Yang, then just kinda up and left, so Taiyang was now a single father then decided "Hey, having a kid with my female teammate worked out so well last time." So he coupled up with Summer, she had Ruby, and raised both Yang and Ruby as her daughters. Then she died.

I just realized that pre-AI Wash was basically Jaune.
I mean, they're even both blondes with multiple sisters (according to the ultimate fan guide, Wash has several sisters)
Also, both are close to a redhead voiced by Jen Brown.